Earnings Per Share - Antidilutive Securities (Details) - shares	3 Months Ended							12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (shares)						299,412		282,801
Class B Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (shares)	12,921,637	16,184,026	17,112,164	17,213,806	17,213,806		17,213,806	15,856,855
Out-of-the-money Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (shares)	446,000	443,000	30,500	754,750				626,500
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (shares)	1,131,760	1,188,987	1,012,916		565,840		377,537	1,009,858